In said earlier-filed application which, so far as relevant is incorporated herein by reference, it is explained that in industrial shaping or finishing steel articles of manufacture they are commonly subjected to grinding operations wherein a coolant comprising water combined with a water miscible or soluble lubricant is employed. As a result a detritus, known as swarf, is produced of metal fragments, abrasive particles and lubricant-coolant residue.
The swarf so produced has heretofore had little value because it cannot be economically recycled to produce useful products. It is explained in our earlier application that the residue of lubricant-coolant has presented a major obstacle to the recovery of the steel particles and/or the abrasive. It is further explained that under usual conditions in which swarf is accumulated or stored, the mixture commonly forms into irregular lumps and as a first step in the treating of such material it is ground, where necessary, to break up lumps, and screened to remove foreign bodies, such as pieces of scrap metal, that may have become mixed with the swarf.
With the process disclosed in our co-pending application, the swarf is first washed with a hydrophilic solvent, such as methanol which dissolves the water phase and certain proprietary additives that may be used in combining the water and mineral oil or other lubricant comprising the coolant-lubricant system, but it does not dissolve the lubricant to any appreciable extent. After agitating the swarf with the methanol, the methanol and water is removed in a well-known manner as by filtration or centrifuging and the swarf, now substantially free of water is washed with a hydrocarbon or chlorinated hydrocarbon to dissolve the lubricant phase of the coolant-lubricant, kerosene being a satisfactory hydrocarbon solvent for this purpose. Usually there are two, and typically more, such washings with removal of the solvent and included lubricant after each washing. The final step involves vaporizing any residual solvent from the cleaned swarf in a retort from which the vapors are condensed to recover the solvent. By subsequent fractionation, the second solvent and lubricant may be separated and the solvent reused. At some stage, depending on whether the abrasives as well as the metal values are to be recovered, separation of the metal abrasive is effected. With steel swarf a magnetic separator is used. It is further explained that where important, mixed abrasive particles, such as silicon carbide and aluminum oxide may be electrostatically separated. The metal is recovered in its finely-divided powdered form ready for use in powder metallurgy and elsewhere.